// ClickedPints.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
    'attribute vec4 a_Position;\n' +
    'void main() {\n' +
    '  gl_Position = a_Position;\n' +
    '  gl_PointSize = 10.0;\n' +
    '}\n';

// Fragment shader program
var FSHADER_SOURCE =
    'precision mediump float;\n' +
    'uniform vec4 u_FragColor;\n' +
    'void main() {\n' +
    '  gl_FragColor = u_FragColor;\n' +
    '}\n';

function main() {
    // Retrieve <canvas> element
    var canvas = document.getElementById('webgl');

    // Get the rendering context for WebGL
    var gl = getWebGLContext(canvas);
    if (!gl) {
        console.log('Failed to get the rendering context for WebGL');
        return;
    }

    // Initialize shaders
    if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
        console.log('Failed to intialize shaders.');
        return;
    }

    // // Get the storage location of a_Position
    var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
    var u_FragColor = gl.getUniformLocation(gl.program, 'u_FragColor');
    console.log('u_FragColor:', u_FragColor);
    if (a_Position < 0) {
        console.log('Failed to get the storage location of a_Position');
        return;
    }

    // Register function (event handler) to be called on a mouse press
    canvas.onclick = clickFun;
    function clickFun(ev){
        click(ev, gl, canvas, a_Position, u_FragColor);
    }
    // Specify the color for clearing <canvas>
    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);
}

var g_points = []; // The array for the position of a mouse press
function click(ev, gl, canvas, a_Position, u_FragColor) {
    var x = ev.clientX; // x coordinate of a mouse pointer
    var y = ev.clientY; // y coordinate of a mouse pointer
    var rect = ev.target.getBoundingClientRect() ;
    x = ((x - rect.left) - canvas.width/2)/(canvas.width/2);
    y = (canvas.height/2 - (y - rect.top))/(canvas.height/2);
    // Store the coordinates to g_points array
    g_points.push(x); g_points.push(y);

    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);
    var len = g_points.length;
    console.log(g_points)
    for(var i = 0; i < len; i += 2) {
        // Pass the position of a point to a_Position variable
        gl.vertexAttrib3f(a_Position, g_points[i], g_points[i+1], 0.0);
        gl.uniform4f(u_FragColor, g_points[i], g_points[i+1], 0.0, 1.0);
        // Draw
        gl.drawArrays(gl.POINTS, 0, 1);
    }
}
